Hyunseog Ryu r.hyunseog at ieee.org
Wed Jul 19 17:03:36 EDT 2006

The Problem is that one of Cisco router doesn't allow user settable MTU 
from FastEthernet interface.

router(config-if)# mtu ?
   <64-42949672295> MTU size in bytes

router(config-if)# mtu 1520
% Interface FastEthernet1/1 does not support user settable mtu.

router(config-if)# ip mtu
  <68-1000000>  MTU (bytes)

router(config-if)# ip mtu 1520
% Invalid IP MTU specified; minimum 68, maximum 1500

Because of this one Cisco router, I couldn't use MPLS from this whole 
I would like to replace this router, but I had no choice.

Another option was using "ip ospf mtu-ignore" from Cisco, but it seems 
that JUNOS doesn't support it.

So I think I'm in deadlock situation until I replaced those problematic 
Cisco router.


Harry Reynolds wrote:
> The last I heard the answer was "no", in part because it breaks section
> 10.6. of the rfc.
> Perhaps you can change the mtu on the JNI to match the cisco?
> Regards
>> -----Original Message-----
>> From: juniper-nsp-bounces at puck.nether.net 
>> [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Hyunseog Ryu
>> Sent: Wednesday, July 19, 2006 1:41 PM
>> To: juniper-nsp at puck.nether.net
>> Subject: [j-nsp] OSPF MTU-IGNORE?
>> Hi Guys,
>> Currently I'm running Cisco/Juniper multi-vendor networks.
>> >From one of ethernet segment, I would like to change MTU for 
>> MPLS network.
>> But the problem is that one of cisco router doesn't allow to 
>> change MTU size for ehternet card.
>> So I would like to use "ip ospf mtu-ignore" command from Cisco.
>> I'm wondering whether Juniper has equivalent command or not.
>> This will disable OSPF MTU mismatch check for OSPF between routers.
>> Thanks.
>> Hyun
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>> juniper-nsp mailing list juniper-nsp at puck.nether.net 
>> https://puck.nether.net/mailman/listinfo/juniper-nsp

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